linux-kernel - Re: [PATCH v6 net-next 17/17] net: qualcomm: add QCA7000 UART driver

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Message-ID: <50e5a442-777f-1516-4e94-16db7fa28f8b@i2se.com>
Date:   Wed, 24 May 2017 11:06:37 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     linux-serial@...r.kernel.org, Jiri Slaby <jslaby@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jakub Kicinski <kubakici@...pl>, devicetree@...r.kernel.org
Subject: Re: [PATCH v6 net-next 17/17] net: qualcomm: add QCA7000 UART driver

Am 23.05.2017 um 23:01 schrieb Lino Sanfilippo:
> On 23.05.2017 21:38, Stefan Wahren wrote:
>>> Lino Sanfilippo <LinoSanfilippo@....de> hat am 23. Mai 2017 um 20:16 geschrieben:
>>>
>>> I suggest to avoid this possible race by first unregistering the netdevice and then 
>>> calling cancel_work_sync().
>> What makes you sure that's safe to unregister the netdev while the tx work queue is possibly active?
> unregister_netdevice() calls netdev_close() if the interface is still up. netdev_close() calls flush_work()
> so the unregistration is delayed until the tx work function is finished. Furthermore both close() and
> tx work are synchronized by means of the qca->lock which also guarantees that unregister_netdevice() wont
> be finished until the tx work is done.
>

Thanks for the explanation. I suspect there could be the same race
between serdev_device_close() and the tx work queue.

So i would propose a variant of your original suggestion:

unregister_netdev(qca->net_dev);

/* Flush any pending characters in the driver. */
serdev_device_close(serdev);
cancel_work_sync(&qca->tx_work);

Since we have the same pattern in the error path of the probe function,
the same applies there.

Stefan